Action sports (e.g., skateboarding, snowboarding, bicycle motocross (BMX), downhill mountain biking, and the like), motorsports (e.g., off-road and on-road motorcycle riding and racing) and traditional contact sports (e.g., football and hockey) continue to grow at a significant pace throughout the world as each of these sports expands into wider participant demographics. While technology and sophisticated training regimes continue to improve the performance capabilities for such athletes/participants, the risk of injury attendant to these activities also increases. To date, helmet-type head protection devices have not experienced any significant new technologies that improve protection of the athlete's head and brain in the event of an impact incident outside the advent of duel density foam liners made of greater thickness utilizing softer foams in general. Current “state of the art” helmets are not keeping pace with the evolution of sports and the capabilities of athletes. At the same time, science is providing alarming data related to the traumatic effects of both repetitive but moderate, and severe impacts to the head. While concussions are at the forefront of current concerns, rotational brain injuries from the same concussive impacts are no less of a concern, and in fact, are potentially more troublesome.
Head injuries result from two types of mechanical forces—contact and non-contact. Contact injuries arise when the head strikes or is struck by another object. Non-contact injuries are occasioned by cranial accelerations or decelerations caused by forces acting on the head other than through contact with another object, such as whiplash-induced forces. Two types of cranial acceleration are recognized, which can act separately or in combination with each other. “Translational” acceleration occurs when the brain's centre of gravity (CG), located approximately at the pineal gland, moves in a generally straight line. “Rotational” or angular acceleration occurs when the head turns about its CG without linear movement of the CG.
Translational accelerations/decelerations can result in so-called “coup” and “contrecoup” head injuries that respectively occur directly under the site of impact with an object and on the side of the head opposite the area that was impacted. By contrast, studies of the biomechanics of brain injury have established that forces applied to the head which result in a rotation of the brain about its CG cause diffuse brain injuries. It is this type of movement that is responsible for subdural hematomas and diffuse axonal injury (DAI), one of the most devastating types of traumatic brain injury.
Referring to FIG. 1, the risk of rotational brain injury is greatest when an impact force 10 is applied to the head or helmet 12 of a wearer from at an oblique angle, i.e., greater or less than 90 degrees to a perpendicular plane 14 drawn through the CG 16 of the brain. Such impacts cause rotational acceleration 18 of the brain around CG, potentially shearing brain tissue and causing DAI. However, given the distribution of brain matter, even direct linear or translational impacts can generate shear forces within the brain sufficient to cause rotational brain injuries. Angular acceleration forces can become greater, depending on the severity (i.e., force) of the impact, the degree of separation of the impact force 10 from 90 degrees to the perpendicular plane 14, and the type of protective device, if any, that the affected individual is wearing. Rotational brain injuries can be serious, long lasting, and potentially life threatening.
Safety helmets generally use relatively hard exterior shells and relatively soft, flexible, compressible interior padding, e.g., fit padding, foam padding, air filled bladders, or other structures, to manage impact forces. When the force applied to the helmet exceeds the capability of the combined resources of the helmet to reduce impacts, energy is transferred to the head and brain of the user. This can result in moderate concussion or severe brain injury, including a rotational brain injury, depending on the magnitude of the impact energy.
Safety helmets are designed to absorb and dissipate as much energy as possible over the greatest amount of time possible. Whether the impact causes direct linear or translational acceleration/deceleration forces or angular acceleration/deceleration forces, the helmet should eliminate or substantially reduce the amount of energy transmitted to the user's head and brain.